


Forthcoming Seminars at F1
Tuesday 11 Dec 2018 11:15  Lucas Hackl (MPQ Garching)  Low energy spectra from variational tangent planes 

Variational methods are extensively used to study properties of ground states and low excited states. By focusing on a suitable submanifold of states, we can overcome the exponential growth of the Hilbert space with the system size. In this talk, I will introduce a geometric framework to approximate the low lying energy spectrum by studying the linearized Hamiltonian flow on the tangent plane at the ground state. The spectrum is then given by the eigenvalues of the covariant derivative on the variational manifold. Using the paradigmatic BoseHubbard model as an example, I will discuss advantages compared to methods based on directly diagonalizing the Hamiltonian restricted to the tangent plane.
Seminar room for physics (JSI main building) 
Seminars Archive
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 11 Dec 2012 15:00  Martin Nuss  Strongly correlated quantum systems out of equilibrium: A variational cluster approach 

Tea room F1. Abstract:
The theoretical understanding of the nonequilibrium behavior of strongly correlated quantum many body systems is a long standing challenge, which has become increasingly relevant with the progress made in the fields of molecular and nano electronics, spintronics, spectroscopy or quantum optics and simulation. Besides seeding the fundamental concepts for promising future applications, developing a sound understanding of the plethora of previously unrecognized effects, arising in a nonequilibrium situation, is currently at the forefront of theoretical research.
We report on the development of nonequilibrium cluster perturbation theory [1], and its variational improvement, the nonequilibrium variational cluster approach [2]. The nonequilibrium extensions of the wellestablished equilibrium theories are based on the Keldysh Greens function method which allows accessing single particle dynamic quantities. These flexible and versatile techniques can in principle be applied to any bosonic and/or fermionic lattice Hamiltonian, including multiband and multiimpurity systems. Within this framework it is possible to work in the thermodynamic limit and therefore exchange particles with a bath and/or dissipate energy. We will highlight the importance of the selfconsistent feedback, introduced in the nonequilibrium variational cluster approach.
We will discuss the performance, open issues and limitations as well as the advantages of the nonequilibrium variational cluster approach on the basis of a single impurity system. Based on the good performance of the variational cluster approach for the single Impurity Anderson model in the equilibrium situation [3], results obtained for the steady state current density as well as the nonequilibrium density of states of a strongly correlated single quantum dot will be presented [4]. These will be benchmarked against data for the quasi stationary state from a real time evolution using matrix product states.
[1] M. Balzer and M. Potthoff, Phys. Rev. B 83, 195132 (2011)
[2] M. Knap, W. von der Linden and E. Arrigoni, Phys. Rev. B 84, 115145 (2011)
[3] M. Nuss, E. Arrigoni, M. Aichhorn and W. von der Linden, Phys. Rev. B 85, 235107 (2012)
[4] M. Nuss, Christoph Heil, Martin Ganahl, Michael Knap, Hans Gerd Evertz, Enrico Arrigoni, Wolfgang von der Linden, to appear in: Phys. Rev. B (2012) 
5 Oct 2012 12:00  Markus Aichhorn  Correlation effects in 3d, 4d, and 5d transition metal oxides 

Physics seminar room (106). Abstract:
Strong electron correlations appear when the kinetic energy in a
system is comparable or smaller than the repulsive Coulomb interaction
energies. Until a few years ago this behavior was attribute in
transition metal compounds almost exclusively to materials with open
3d shells, and just a few studies on a limited amount of systems have
been done outside of this play ground.
Only recently, it has been noted that also systems with 4d or even 5d
electronic states in the conduction bands can show very interesting
and unexpected behavior. Applying fully abinitio electronic structure
calculations by combining densityfunctional theory with the dynamical
mean field theory, we will discuss the following topics. First, we
will focus on ruthenate materials, were heavy electron masses and very
low coherence scales have been found in experiments. Second, we will
look at the extraordinarily high magnetic transition temperature in
technetium compounds. Last but not least, we will discuss the
insulating states in iridium compounds. The origin of these effects
will be traced back to subtle interplay of several energy scales,
i.e. Coulomb, Hund, SpinOrbit, etc. interactions.

4 Sep 2012 15:00  Artem Badasyan  Osmotic Pressure Induced Coupling between Cooperativity and Stability of a HelixCoil Transition 

Physics seminar room (106). 
28 Aug 2012 15:00  Thomas Pruschke  The Kondo lattice model in the dynamical meanfield approach 

Tea room F1. 
20 Jul 2012 11:00  prof. Takami Tohyama  Resonant inelastic xray scattering (RIXS) in cuprates and iron pnictides 

Tea room F1. 
27 Jun 2012 11:30  Vikram Soni  New Physics from Magnetars 

We shall walk you through a plausible theory of the origin of magnetars – neutron stars with surface magnetic fields of 10^14(15) gauss and flares that emit 10^47 ergs of energy in a fraction of a second. In our picture magnetars are most massive neutron stars that carry a magnetized core created by a high density strong interaction phase transition. The magnetic core so created is first screened by the surrounding high conductivity plasma. It is then transported to the crust and breaks through the crust to get out to the surface. 
6 Apr 2012 11:00  Christos N. Likos  Electrostatics and soft matter: from starbranched polyelectrolytes to patchy colloids 

Kolarjeva predavalnica (skupni seminar z Odsekom za elektronsko keramiko K5):
In
this
talk,
we
will
first
review
the
Physics
of
starbranched
polyelectrolytes
(SBP)
demonstrating
that
their
conformations
and
interactions
are
dictated
by
electrostatics
in a
rather
subtle
fashion,
whereas
the
mutual
repulsions
of
the
charged
monomers
play
the
decisive
role
in
stretching
the
arms,
the
subsequent
effective
interactions
between
SBPs
is
dominated
by
the
entropic
repulsion
between
the
counterions
adsorbed
in
the
interior
of
the
SBPs
[1].
We
will
present
the
extensions
of
the
theory
to
both
spherical
polyelectrolyte
brushes
[1]
and
to
rigid
chains
[2,3],
proceeding
to
the
investigations
on
adsorption
of
PEstars
onto
oppositely
charged
flat
surfaces
[4]
or
colloidal
spheres
[5].
We
argue
that
the
complexes
that
form
can
be
viewed
as
a
novel
type
of
patchy
colloids
[6],
and
we
present
an
efficient
way
of
coarsegraining
their
effective
interactions
to
a
manageable
yet
realistic
mesoscopic
model
[7].
Finally,
we
discuss
ongoing
work
on
soft
patchy
colloids,
emerging
out
of
endfunctionalized
starbust
block
copolymers
[8].
[1]
A.
Jusufi
and
C.
N.
Likos,
Rev.
Mod.
Phys.
81,
1753
(2009).
[2]
K.
Kegler,
M.
Konieczny,
G.
DominguezEspinosa,
C.
Gutsche,
M.
Salomo,
F.
Kremer,
and
C.
N.
Likos,
Phys.
Rev.
Lett.
100,
118302
(2008).
[3]
A.
Wynveen
and
C.
N.
Likos,
Soft
Matter
6,
163
(2010).
[4]
M.
Konieczny
and
C.
N.
Likos,
Soft
Matter
3,
1130
(2007).
[5]
C.
N.
Likos,
R.
Blaak,
and
A.
Wynveen,
J.
Phys.
Condens.
Matter
20,
494221
(2008).
[6]
E.
Bianchi,
R.
Blaak,
and
C.
N.
Likos,
Phys.
Chem.
Chem.
Phys.
13,
6397
(2011).
[7]
E.
Bianchi,
G.
Kahl,
and
C.
N.
Likos,
submitted
(2011).
[8]
B.
Capone,
C.
N.
Likos,
and
F.
LoVerso,
in
preparation.
more... 
20 Mar 2012 15:00  Adriano Amaricci  Nonequilibrium stationary state formation in driven Hubbard model 

Physics seminar room (106). Abstract:
I shall present a recent work concerning the nonequilibrium dynamics of a strongly correlated electrons systems in a static electric field, with the aim of identifying the conditions to reach a nonequilibrium stationary state (NSS).
I show that, for a generic electric field, the convergence to a stationary state requires the coupling to a thermostating bath, absorbing the work done by the external force. By following the realtime dynamics of the system, I also show that coupling to bath provides an essentially sufficient condition, i.e. NSS can be reached for almost any value of dissipation. I characterize the properties of the NSS in terms of some physical observables, pointing out the existence of an analogue of the Pomeranchuk effect. Finally, I map out a phase diagram of the system and I identify a dissipation regime for which steady current is largest for a given field.

14 Mar 2012 15:00  Hantao Lu  Photoinduced phase transition in onedimensional extended Hubbard model 

Tea room F1. Abstract:
We illustrate one interesting example of photoinduced phase transitions in lowdimensional strongly correlated systems. By using timedependent Lanczos method, the nonequilibrium process of the halffilled onedimensional Hubbard model, driven by external laser pulse, is investigated. Charge carriers, namely, holons and doublons, can be generated during the pump. Starting from the spindensitywave (SDW) side, we find that when the system is close to the boundary, by tuning the laser frequency and strength, a sustainable charge order enhancement, which is absence in the Mott insulating phase, can be spotted even after the pulse turned off. This phenomenon has its root in the spectral properties. From the spectrum analysis on small size systems, it can be shown that with increasing the nearestneighbour interactions, accordingly, chargeorder favorite eigenstates move from high energy regime to less dense low energy part, which leaves themselves prone to be picked up by laser pulse. The conditions of the emergence of charge density order and possible experimental realizations are discussed. 
13 Mar 2012 15:00  Wataru Koshibae  Real time simulation of photoexcited state in junction of doubleexchange systems: Theoretical design of highefficiency solarcell 

Physics seminar room (106). Abstract:
The photoinduced insulatortometal (IM) transition is studied
by the numerical simulation of realtime quantum dynamics
of a doubleexchange model.
We find a characteristic multiplication of particlehole (ph) pairs
by a ph pair of high energy during the IM transition.
To examine the conversion from the ph pairs into electric energy,
we perform the numerical study on the junction systems combined
by the double exchange models.
The numerical results reveal:
(i) the threshold behavior with respect to the intensity and energy of light,
(ii) ph pairs are well separated and pair annihilation is suppressed,
(iii) enhancement of collected carrier by metastability of IM transition.
The energy window of the ph pair multiplication is also important
for efficiency of the energy conversion.
In the light of the theory,
we propose a path to highefficiency solarcell by interacting electrons. 
6 Mar 2012 15:00  Luca Tubiana  Geometrical and topological entanglement in packaged viral DNA 

Physics seminar room (106). Abstract:
The packing of DNA inside bacteriophages arguably yields the simplest example of genome organisation in nature
and understanding its physics is of primary importance for both the biophysical implications and the possible applicative ramifications [13].
Cryoem studies on bacteriophages epsilon15 [4] and phi29 [5] showed that DNA is neatly ordered in concentric shells close to the capsid wall,
while an increasing level of disorder was measured when moving away from the capsid internal surface. On the other hand the detected spectrum of
knots formed by DNA that is circularised inside the P4 viral capsid showed that DNA tends to be knotted with high probability, with a knot
spectrum characterized by complex knots and biased towards torus knots and against achiral ones [6,7].
We show, using advanced stochastic simulation techniques, that both the shell ordering and the knot spectrum can be reproduced quantitatively if
one accounts for the preference of contacting DNA strands to juxtapose at a small twist angle, as in cholesteric liquid crystals. Furthermore the
DNA knots we observe are strongly delocalized and, intriguingly, this is shown not to interfere with genome ejection out of the phage [8].
Starting by this observation, we investigate the interplay of geometrical and topological entanglement in knotted DNA rings confined inside a
spherical cavity, using stringent and robust algorithms for locating knots [9]. We show that the complex interplay between the length of the
knotted portion of DNA, the contour length of the DNA ring, and the radius of the enclosing sphere can be encompassed by a simple scaling argument
based on deflection theory [10].
References
[1] Earnshaw WC, Harrison SC (1977) DNA arrangement in isometric phage heads. Nature 268:598602.
[2] Gelbart WM, Knobler CM (2009) Virology. pressurized viruses. Science 323:16821683.
[3] Siber A, Bozic AL and Podgornik R (2011) Phys Chem Chem Phys. DOI:10.1039/c1cp22756d
[4] Jiang W, Chang J, Jakana J, Weigele P, King J and Chiu W (2006) Nature 439: 612616
[5] Comolli LR, Spakowitz AJ , Siegerist CE, Jardine PJ, Grimes S, Anderson DL, Bustamante C, Downing KH (2008) Virology 371:267277
[6] Arsuaga J, Vazquez M, Trigueros S, Sumners D, Roca J (2002) Proc Natl Acad Sci U S A 99:53735377.
[7] Arsuaga, J et al. (2005) Proc Natl Acad Sci U S A 102:91659169.
[8] Marenduzzo D, Orlandini E, Stasiak A, Sumners DW, Tubiana L, Micheletti C (2009) Proc Natl Acad Sci U S A 106:2226922274.
[9] Tubiana L, Orlandini E, Micheletti C (2011) Prog Theor Phys supp 191:192204
[10] Tubiana L, Orlandini E, Micheletti C (2011) PRL 107:188302188305 
17 Feb 2012 13:00  Professor Stefan Thurner  Entropy for complex systems  exploring the world beyond Shannon 

Tea room F1. Abstract:
In information theory the socalled 4 ShannonKhinchin (SK) axioms uniquely determine Boltzmann Gibbs entropy
as the oneandonly possible entropy. Physics is different from information in the sense that physical systems can be nonergodic.
To describe strongly interacting statistical nonergodic systems i.e. complex systems with
a thermodynamical framework, it becomes necessary to introduce generalized entropies.
A series of such entropies have been proposed in the past. Until now the understanding of the fundamental origin
of these entropies and its deeper relations to complex systems is unclear.
Nonergodicity explicitly violates the fourth SK axiom. We show that violating this axiom and keeping the
other three axioms intact, determines an explicit form of a generalized entropy, $Ssim sum_i Gamma (d+1,1clog p_i)$,
where $c$ and $d$ are scaling exponents, uniquely describing a statistical system; Gamma is the incomplete Gamma function.
All recently proposed entropies appear to be special cases. We next prove that each (!) statistical system is uniquely characterized by
the pair of the two scaling exponents (c,d), which define equivalence classes for all (!) interacting and noninteracting systems, i.e. no other possibilities for entropies exist.
The corresponding distribution functions are special forms of Lambert$W$ exponentials containing  as special
cases Boltzmann, stretched exponential and Tsallis distributions (powerlaws)  all abundant in nature.
This is an ab initio justification of the necessity of generalized entropies.
We next show how the phase space volume of a system is related to its (generalized) entropy.
We illustrate this with physical examples of spin systems on constantconnectency networks and accelerating random walks. 
27 Jan 2012 12:00  John H. Jefferson  Quantum Dot Spin Cellular Automata for Realizing a Quantum Process 

Tea room F1. Abstract:
The singlet and triplet states of a twoelectron quantum dot can be used as a qubit, whose spin can be measured by a single charge detection. I will show how to implement single and two qubit quantum gates by coupling such dots together to form quantum cellular automata, driven by the coherent dynamics of the electrons. Such automata therefore provide a rapid, deterministic and stable way of performing universal quantum computation. 




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